The pathogenesis of autoimmunity in New Zealand mice is still uncertain; however, advances are being made. Genetic, viral and immunologic factors appear to be involved. The immunologic factors are complex. These include excessive B-cell activation and impaired T-cell suppressive activity. The loss of T-cell activity is related to a deficiency of suppressor cell precursors. Antibodies to T cells produce an accelerated loss of suppressor cells and their precursors. Furthermore, sex hormones modulate the severity of the disease.